I just got my OC-5 in yesterday, and fired it up this morning. It's on my board - my TC sub 'n up is now mothballed. One of the churches I play at, the worship leader likes a bit of sub stuff here and there, so this is an occasional thing for me. Although the OC-5 will do more than one thing, the one thing I need it to do - just add some sub octave, it does very well.
The OC-5 is the first octaver I've tried that just works - you don't have to play "special", you just do your thing, and it does what it's supposed to. The TC sub'n up was close, the OC-5 is just...there. Mine is set in poly mode, with the direct level at noon, and the -1 octave level at 9 O'Clock (the other two knobs are fully ccw) - that's a nice mix with plenty of sub stuff going on.
The only thing I need to pay attention to is not to wander down on the B string while it's on - it'll happily track all the way down, and you don't quite want that. I'll have to alert the FOH guy that he NEEDS a high pass - just in case.